Hi stefano. Good to have you here.
The basic difference in Test cricket and ODI cricket is its duration - one lasts 5 days with minimum 450 overs(weather permitting that is) and the other lasts 100 overs- both sides ofcouse.
If you are wondering what an over is, an 'over' is a collection of six consecutive legal deliveries bowled by the bowler- inorder for a delivery to be legal, it can only bounce once before reaching the batsman(else it is a deadball and the ball is rebowled), the bowler's foot cannot cross a line ( else it is a noball and there is a 1 run penalty + number of runs a batsman scores off of it and the ball is rebowled) and it cannot be bowled so wide that the batsman cannot reach it ( else it is a wide and it is a 1 run penalty with the ball being rebowled).
There are some other minor tinklings in the noball rule - for example, in ODIs, you can bowl 1 bouncer per over and in Tests you can bowl 2 bouncers per over - anything more is deemed a 'noball' and the bowler is warned.
Repeated warnings might see the bowler's right to bowl revoked.
A bouncer is a ball that hits the pitch quite some way before reaching the batsman(usually) and rears to shoulder-height or above.
In one day internationals ( short form is ODIs or LOIs), the objective is to score more than the opposition in the allocated 50 overs.
So basically if you score 259/8, i have to score 260. Doesnt matter if i've lost no wickets or 9 wickets - if i lose 10 wickets( 10 outs), then my team is allout and it can only be a tie or a loss(depending on when you lost your last wicket).
The bowlers also have a limitation in that they are allowed a maximum of 10 overs per match. So in the least you have to have 5 players capable of bowling but often you want a sixth or a seventh one to relieve a bowler having a bad day.
Since ODI cricket is about scoring more runs in a limited time, your average( that is how much runs you score on average per dismissal) and your striek rate ( how many runs you score per balls faced) is on the premium.
Conventionally, a batsman with 40+ average and 80+ strike rate is deemed an alltime great in the annals of the game.
A 35+ average and a 75-ish strike rate is considered an extremely good player and a 30+ average with a 70-75 average is considered......well...average.
For a bowler, an average of around 21-22 (that is 21-22 runs conceded per wicket taken) and an economy rate of less than 4 runs per over is considered in alltime great category.
a sub 25 average with a 4-4.5 economy rate is considered extremely good and an average that is near 30 with an economy rate higher than 4.5 is seen as average.
Ofcourse, there are different ways of looking at statistics- in my opinion,your performance away from home and your performance against the best nations must be weighed appropriately.
In test cricket, time permitting(and some rules permitting), each team bats twice and the objective is to dismiss the opposition for a lower combined total than your team's.
As such, you have to dismiss 20 players ( 10 players per innings) to achieve that.
Since it is played over 5 days and bowlers have no restrictions- they can bowl as many overs as the team(captain/coach) deems, it is a much more technically challenging game, giving rise to elaborate plans and extremely good mental battle(as cricket is a very cerebral game). However, there are certain times when a team isnt required to bat twice- its a choice mind you.
Lets say my team bats first ( who bats first and who doesn't is always decieded by a simple coin-toss) and scores 600. Your team, in their first innings(remember-max 2 innings) scores 400 or less, (basically your team's first innings dig is adrift of mine's by 200 or more runs), i have the option not ask my team to go out and bat immediately but ask you to bat again for your second innings.This is called enforcing the 'follow on'. Often while a team is batting for second, in their first dig, you see a 'follow on target'. Which is how many runs they need to score inorder to prevent following on and the in order to save follow on(ie not present the opposition with the option to make you follow-on), your team's score must be within 199 runs or lower of the opposition's. Should you score more than the 200 run(or more) deficit in your second dig, then my team has to chase that down to win the match.
For example, my team scores 600 and your team scores 400. You are 200 or more runs adrift, then i ask you to bat again (remember- it isnt a hard and fast rule but merely an option i can choose to exercise). In your second dig, your team scores 335. So your aggregate is 135 over mine and thus my objective is to score 136 to win that game. Ofcourse, the game has 5 days allocated to it with 90 overs(weather permitting) to be bowled per day. As such, there may not be enough time in the 5th day for me to chase the target or for you to take all 10 wickets in my second dig. For eg, there could only be 20 overs left for my second dig and lets say my team finishes at 64/3. As such, since my team hasn't reached the target inorder to win and your team hasn't taken all 10 wickets to win, the match is a draw.
As such, you see draws in Test cricket quiete often. You do not see draws in ODI cricket, because the rules are more result-oriented- your team either overhauls my team's target or your team loses.
In rare occasions, both in Test cricket and in ODI cricket, you have a tie. Inorder to have a tie in test cricket, the aggregate scores must be level with the last batting team allout(ie, all 10 wickets have fallen). In ODI cricket, the scores must be level with the last legal delivery in the team batting second's inning has been bowled.
I think there has been only 3 tied tests and less than 10 tied ODIs in the history of the game.
Another option you have is to declare your innings closed. Basically, a team (ie a captain) can deciede to close the team's batting innings at any point he or she desires. In ODI cricket, it is almost never excercised, since the objective is to score as much runs possible and you got a 50 overs to bowl out your opposition anyways- more runs they chase the better. But in test cricket, since one has to keep an eye on how much time is left available in the game, you often see declarations.
For example, lets say your team has really poor bowlers. I score 600 in my first dig and you stutter to 250. I deciede not to enforce the follow-on and i go out to bat. My team is already 350 runs ahead and by the end of the 4th day, my team has scored 350/5 in its second dig, a total lead of 700 runs. While all my team's wickets hasn't fallen and my team can bat on as long as they wish(until last man is dismissed), it would be prudent for my team to declare their innings closed and leave you with 700 runs to chase. It would be prudent becase my objective is to win the game and i do need to allocate some time to take the opposition's 10 wickets- else they will just draw the game.
Since the objective of the game is to dismiss 20 players for a lower aggregate total, the ability to take wickets for lower scores(average of the bowler) is extremely important.
The no ball and wide rules carry over to Test cricket with the abovementioned slight difference in the noball rule.
Typically in test cricket a batsman's strike rate isnt very important-he has loads of time to make his runs and thus runs are of importance. That is not to say that a high strike rate isn't handy. A 50+ batting average is deemed in the alltime great category for a batsman and a 21-22 or under bowling average is deemed in the alltime great category for a bowler.
For a bowler, his ability to take wickets is more important than his ability to be miserly(in my opinion), as such his strike rate matters more than his economy rate. Typically, fast bowlers have a lower strike rate and average than spinners, though spinners have their perks. Since it is less stenous to bowl, a spinner can operate for a longer period of time and usually has a higher wickets per match rate. They are also vital on certain wickets and most of the time,give the team the necessary variety to be competitive.
As such, for a fast bowler, a sub-55 strike rate is deemed excellent and a sub 50 strike rate is deemed in the alltime great category.
For a spinner, it is a bit more blurred, as the role of a spinner and the approach of a spinner has changed a lot in the last 40 years.Decades ago, an average just under 30 and a strike rate of around 65-70 were deemed alltime great with low 30s average and a strike rate slightly over 70 deemed worldclass.
Of recent times, an average of high 20s/25 or under is seen as alltime great with a strike rate of 65 or under also falling into that category.
An average of low 30s with a strike rate in high 60s is seen as worldclass.
Ofcourse, as in ODI cricket, in my opinion, the appropriate statistics should always be weighed proportionately by the appropriate factors.
I hope that this post has helped you further your understanding of cricket. Cheers!